A signature (from Latin signare, "sign") is a handwritten (and sometimes stylized) depiction of someone's name, nickname or even a simple "X" that a person writes on documents as a proof of identity and intent. The writer of a signature is a signatory. Like a handwritten signature, a signature work describes the work as readily identifying its creator.
For example, the role of a signature in many consumer contracts is not solely to provide evidence of the identity of the contracting party, but rather to additionally provide evidence of deliberation and informed consent. This is why the signature often appears at the bottom or end of a document.
In many countries, signatures may be witnessed and recorded in the presence of a Notary Public to carry additional legal force. On legal documents, an illiterate signatory can make a "mark" (often an "X" but occasionally a personalized symbol), so long as the document is countersigned by a literate witness. There are many other terms which are synonymous with 'signature'. In the United States, one is John Hancock, named after the first of the signatories of the United States Declaration of Independence.
The signature of a famous person is sometimes known as an autograph, and is then typically written on its own or with a brief note to the recipient. Rather than providing authentication for a document, the autograph is given as a souvenir which acknowledges the recipient's access to the autographer.
In the United States, some states’ legal definition of a signature defines a signature to mean "any memorandum, mark, or sign made with intent to authenticate any instrument or writing, or the subscription of any person thereto." In the context of one particular statute, a signature doesn’t have to be the popular notion of a written name, but may be other methods of authentication; the intent of any mark or memorandum makes a signature.
Many individuals have much more fanciful signatures than their normal cursive writing, including elaborate ascenders, descenders and exotic flourishes, much as one would find in calligraphic writing. As an example, the final "k" in John Hancock's famous signature on the US Declaration of Independence loops back to underline his name. This kind of flourish is also known as a paraph.
More recently, Members of Congress in the United States have begun having their signature made into a True Type Font file. This allows staff members in the Congressman's office to easily reproduce it on correspondence, legislation, and official documents.
Several cultures whose languages use writing systems other than alphabets do not share the Western notion of signatures per se: the "signing" of one's name results in a written product no different from the result of "writing" one's name in the standard way. For these languages, to write or to sign involves the same written characters. Three such examples are Chinese, Japanese, and Korean. In Asian culture, people typically use name-seals or inkan with the name written in tensho script (seal script) in lieu of a handwritten signature (also see Calligraphy).
In e-mail and newsgroup usage, another type of signature exists which is independent of one's language. Users can set one or more lines of custom text known as a signature block to be automatically appended to their messages. This text usually includes a name, contact information, and sometimes quotations and ASCII art. A shortened form of a signature block, only including one's name, often with some distinguishing prefix, can be used to simply indicate the end of a post or response. Some web sites also allow graphics to be used. Note, however, that this type of signature is not related to electronic signatures or digital signatures, which are more technical in nature and not directly readable by human eyes.
By analogy, the word "signature" may be used to refer to the characteristic expression of a process or thing. For example, the climate phenomenon known as ENSO or El Niño has characteristic modes in different ocean basins which are often referred to as the "signature" of ENSO.